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Abstract:

There is provided a titanium alloy for corrosion-resistant materials,
which contains 0.01-0.12% by mass in total of at least one of platinum
group elements; at least Si and one of, or both of, Sn and Mn, selected
from the group consisting of Al, Cr, Zr, Nb, Si, Sn and Mn, wherein the
total content of Al, Cr, Zr, Nb, Si, Sn and Mn is 5% by mass or less; and
the residue comprising Ti and impurities.

Claims:

1. A titanium alloy for corrosion-resistant materials, which contains
0.01-0.12% by mass in total of at least one of platinum group elements;
at least Si and one of, or both of, Sn and Mn, selected from the group
consisting of Al, Cr, Zr, Nb, Si, Sn and Mn, wherein the total content of
Al, Cr, Zr, Nb, Si, Sn and Mn is 5% by mass or less; and the residue
comprising Ti and impurities.

2. A titanium alloy for corrosion-resistant materials, which contains
0.01-0.12% by mass in total of at least one of platinum group elements,
0.05-2.00% by mass in total of one of, or both of, Co and Ni, ; at least
Si and one of, or both of, Sn and Mn, selected from the group consisting
of Al, Cr, Zr, Nb, Si, Sn and Mn, wherein the total content of Al, Cr,
Zr, Nb, Si, Sn and Mn is 5% by mass or less; and the residue comprising
Ti and impurities.

[0003]Titanium forms thereon an oxidized film and therefore is not easily
corroded as compared with general metals, so that it is widely used in a
place requiring corrosion resistance. However, in this intended use,
there is a demand for titanium having more excellent corrosion
resistance, and in order to deal with it, corrosion resistance is
improved hitherto by adding another element to titanium.

[0004]For example, as titanium having improved corrosion resistance,
Ti--Pd alloys, which are also prescribed in JIS 11 type, 12 type and 13
type, are known. These are alloys containing 0.12-0.25% by mass of Pd in
pure titanium. Also, it is conventional to contain therein Co, Ni or the
like other than Pd (cf. Patent Documents 1 and 2).

[0005]Meanwhile, titanium has excellent characteristics as compared with
general metals, and specifically it has not only excellent corrosion
resistance but also a light weight and a high strength, and therefore
various alloys are used in various applications, such as sports goods
such as golf clubs and bicycles. However, titanium alloys are expensive
compared with general metals, and in these days, utilization of low cost,
recycled titanium alloys, which are obtained by recycling not only sponge
titanium produced from titanium ores, but also titanium alloys, which
were once introduced into markets and had become out of use, are now
being studied.

[0006]However, when even a small amount of another element is mixed in
titanium for which corrosion resistance is required as mentioned above,
corrosion may occur starting at such an element, and therefore recycled
titanium alloys are not used for titanium alloys for corrosion-resistant
materials. Furthermore, platinum group elements, such as Pd, are
generally expensive compared with titanium and therefore titanium alloys
for corrosion-resistant materials have been very expensive in the past.

[0007]In other words, conventional titanium alloys for corrosion-resistant
materials have a problem in that they cannot be produced at low cost
while maintaining the capability to suppress the deterioration of
corrosion resistance.

[0010]In consideration of the above problems, it is an object of the
present invention to provide a titanium alloy for corrosion-resistant
materials that is capable of being produced at low cost while maintaining
the capability to suppress the deterioration of corrosion resistance.

[0011]The present inventors intensively studied in order to solve the
above problems, consequently found that it is possible to suppress the
deterioration of corrosion resistance when a certain amount or less of at
least one of Al, Cr, Zr, Nb, Si, Sn and Mn is contained in a titanium
alloy, and thus achieved the present invention.

[0012]Specifically, according to the present invention, there is provided
a titanium alloy for corrosion-resistant materials, which contains
0.01-0.12% by mass in total of at least one of platinum group elements;
at least Si and one of, or both of, Sn and Mn, selected from the group
consisting of Al, Cr, Zr, Nb, Si, Sn and Mn, wherein the total content of
Al, Cr, Zr, Nb, Si, Sn and Mn is 5% by mass or less; and the residue
comprising Ti and impurities.

[0013]By containing further Si and one of, or both of, Sn and Mn in a
titanium alloy is meant that these elements are present in the titanium
alloy in an amount exceeding the unavoidable level. The content of the
above mentioned Al, Cr, Zr, Nb, Si, Sn and Mn can be measured by using a
conventionally used analytic instrument. Usually, the contents, as the
unavoidable levels, of these elements present in a titanium alloy are, at
maximum, Al: 0.007% by mass, Cr: 0.007% by mass, Zr: 0.001% by mass, Nb:
0.001% by mass, Si: 0.004% by mass, Sn: 0.001% by mass and Mn: 0.001% by
mass, respectively. Accordingly, by containing Al, Cr, Zr, Nb, Si, Sn and
Mn in a titanium alloy is meant in the specification of this application
that these elements each are present in the titanium alloy in an amount
exceeding the corresponding amount.

Advantages of the Invention

[0014]According to the present invention, Al, Cr, Zr, Nb, Si, Sn or Mn is
contained in a titanium alloy for corrosion-resistant materials, so that
it is possible to reuse recycled titanium alloys coming from products in
which at least one of Al, Cr, Zr, Nb, Si, Sn and Mn is used. In addition,
according to the present invention, 0.01-0.12% by mass in total of at
least one of platinum group elements is contained in the titanium alloy
for corrosion-resistant materials, and the total content of Al, Cr, Zr,
Nb, Si, Sn and Mn is 5% by mass or less. Whereby, it is possible to
suppress the deterioration of corrosion resistance.

[0015]In other words, it is possible to provide a titanium alloy for
corrosion-resistant materials that is capable of being produced at low
cost while maintaining the capability to suppress the deterioration of
corrosion resistance.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0016]Now, the description will be made for a preferred embodiment of a
titanium alloy for corrosion-resistant materials. First, the description
will be made for the amount of each element contained in a titanium alloy
for corrosion-resistant materials and the reason for determining the
amount thereof.

[0017]A titanium alloy for corrosion-resistant materials of this
embodiment usually contains a platinum group element, one of, or both of,
Co and Ni, at least one of Al, Cr, Zr, Nb, Si, Sn and Mn, and the residue
comprising Ti and impurities.

[0018]The platinum group element is an essential component of a titanium
alloy for corrosion-resistant materials, and the content thereof is
0.01-0.12% by mass. The content of the platinum group element is
0.01-0.12% for the reason that when the platinum group element is less
than 0.01% by mass, the corrosion resistance of the titanium alloy for
corrosion-resistant materials does not reach a satisfactory level, which
may cause corrosion, and on the other hand, even when the content thereof
exceeds 0.12% by mass, it cannot be expected to have the corrosion
resistance improved as the increase of the content thereof, and in
addition, there is a possibility of increasing the cost of a titanium
alloy for corrosion-resistant materials.

[0019]As this platinum group element, it is possible to use Ru, Rh, Pd,
Os, Ir and Pt, and preferably use Pd.

[0020]Co and Ni are optional components, and the content thereof is
0.05-2.00% by mass. They are contained in the amount of 0.05-2.00% by
mass, thereby producing an advantage of further improving the corrosion
resistance while increasing the strength of the titanium alloy for
corrosion-resistant materials. When the total amount of Co and Ni is less
than 0.05% by mass, it is difficult to produce the advantage of further
improving the corrosion resistance while increasing the strength of the
titanium alloy.

[0021]Si, and one of, or both of, Sn and Mn are essential components of a
titanium alloy for corrosion-resistant materials, whereas Al, Cr, Zr and
Nb may not necessarily be contained. The total content of Al, Cr, Zr, Nb,
Si, Sn and Mn is 5% by mass or less. These elements are contained in such
a range for the reason that when the total content of Al, Cr, Zr, Nb, Si,
Sn and Mn exceeds 5%, the corrosion resistance of the titanium alloy for
corrosion-resistant materials is deteriorated, which causes corrosion.
From these points of view, the total content of them is preferably 3% or
less, and more preferably 2% or less.

[0022]Examples of impurities include unavoidable impurities such as C, O,
H and Fe, and a small amount of another element may be contained in the
titanium alloy for corrosion-resistant materials to such an extent as not
to deteriorate the advantages of the present invention. Especially, V, Mo
and W are known as the elements causing less influences on the corrosion
resistance, and can be contained in a titanium alloy for
corrosion-resistant materials as long as the total content thereof is
about 5% by mass or less.

[0023]The titanium alloy for corrosion-resistant materials mentioned above
is preferably used for conduits, heat exchangers, electrolysis vessels
and the like of such as a nickel refining plant, which are used in
environments, in which they are exposed to concentrated sulfuric acid,
nickel sulfate or nickel chloride at about 250° C.

Examples

[0024]Now, the description will be made for the present invention in more
detail with reference to examples without intention to limit the present
invention thereto.

[0026]Titanium alloys for corrosion-resistant materials are prepared by
adjusting samples for evaluation on corrosion resistance of the
respective Examples and Comparative Examples, using pure titanium and the
respective components so as to have the components of Tables 1 and 2
contained in the amounts of Tables 1 and 2. For Comparative Example 1,
pure titanium is used.

[0027]First, the titanium alloy of each composition is produced with a
size having a thickness of 20 mm, a width of 70 mm and a length of 90 mm
by melting through button arc melting.

[0028]Then, the thus produced pieces each are hot rolled into 3 mm
thickness, and then acid-washed, thereby removing scale from the surface,
and cut into a test piece having a width of 50 mm and a length of 100 mm.
Then, one side of this test piece is polished with a #200 polishing
sheet, while the lateral and rear sides thereof were sealed with a
sealing agent, thereby allowing only the polished surface to be exposed
to the surface. Thus, each sample for evaluation of corrosion resistance
is prepared.

[0029]As a conventional titanium alloy for corrosion-resistant materials
produced from sponge titanium or the like, a titanium alloy for corrosion
resistance (Conventional Examples 1-4) containing the components shown in
Table 3 are prepared and evaluated in the same manner as in Examples and
Comparative Examples.

[0031]The samples of Reference Examples, Examples, Comparative Examples
and Conventional Examples for evaluation on corrosion resistance each are
immersed in 20% nickel chloride solution at 100° C. for 100 hours,
and the surface of each of the samples are observed by eyes and an
optical microscope. Thus, the surface texture is evaluated. According to
the result of the evaluation, it is determined as "∘" for a
sample in which no change is confirmed between its initial surface
condition and its surface condition after the immersion in the nickel
chloride solution, as "Δ" for a sample in which increase of
unevenness or the like is slightly confirmed therebetween, and as
"×" for a sample in which increase of unevenness or the like is
apparently confirmed therebetween. The results are shown in Table 4.

[0032]The weight of each sample for evaluation of corrosion resistance is
measured before and after the immersion in the nickel chloride solution
by using an electronic balance that is capable of measuring the weight
with the unit of 0.1 mg, and the difference thereof is calculated as a
weight reduction (ΔM). The reduced amount is calculated by the
following expression based on the surface area (S) of each sample for
evaluation of corrosion resistance before the immersion.

Reduced amount (g/m2)=ΔM(g)/S(m2)

[0033]The results are shown in Table 4.

[0034](Heated-Sulfuric-Acid-Resistance Test)

[0035]The samples of Reference Examples, Examples, Comparative Examples
and Conventional Examples for evaluation on corrosion resistance each are
immersed in 5% sulfuric acid solution at 240° C. for 1 hour, and
the reduced amount is determined by calculation in the same manner as in
the nickel-chloride-resistance test. The results are shown in Table 4.

[0036](Heated-Hydrochloric-Acid-Resistance Test)

[0037]The samples of Reference Examples, Examples, Comparative Examples
and Conventional Examples for evaluation on corrosion resistance each are
immersed in boiled 10% hydrochloric acid solution for 1 hour, and the
reduced amount is determined by calculation in the same manner as in the
nickel-chloride-resistance test. The results are shown in Table 4.

[0038](Clearance-Corrosion-Resistance Test)

[0039]Two samples of each of Reference Examples, Examples, Comparative
Examples and Conventional Examples are overlapped each other with the
surfaces thereof facing each other, and are immersed in 20% NaCl solution
at 90° C., adjusted to a pH value of 1 by hydrochloric acid, for
100 hours. Thus, the clearance-corrosion-resistance test is performed. In
the same manner as in the nickel-chloride-resistance test, it is
determined as "∘" for a sample in which no change is
confirmed between its surface conditions before and after the test, as
"Δ" for a sample in which increase of unevenness or the like is
slightly confirmed therebetween, and as "×" for a sample in which
increase of unevenness or the like is apparently confirmed therebetween.
The results are shown in Table 4.

[0040]From Table 4, it is also appreciated that a titanium alloy for
corrosion-resistant materials containing 0.01-0.12% by mass in total of
at least one of platinum group elements; Si and one of, or both of, Sn
and Mn; and the residue comprising Ti and impurities, in which the total
content of Al, Cr, Zr, Nb, Si, Sn and Mn is 5% by mass or less, or a
titanium alloy for corrosion-resistant materials containing 0.01-0.12% by
mass in total of at least one of platinum group elements; 0.05-2.00% by
mass in total of one of, or both of, Co and Ni; Si and one of, or both
of, Sn and Mn; and the residue comprising Ti and impurities, in which the
total content of Al, Cr, Zr, Nb, Si, Sn and Mn is 5% by mass or less, is
excellent in corrosion resistance compared with the respective
Comparative Examples, and has corrosion resistance equivalent to that of
a conventional titanium alloy for corrosion-resistant materials using
sponge titanium.

[0041]In other words, it is appreciated that the titanium alloy for
corrosion-resistant materials of the present invention is capable of
suppressing deterioration of corrosion resistance even though it uses
recycled titanium alloys or the like, and thus being produced at low cost
while maintaining the capability to suppress the deterioration of
corrosion resistance.